It is well known to copy an original image using a photographic printing technique in which a photosensitive element is exposed to light from the original image. In contact printing an original image is printed by positioning a light sensitive element in contact with an original transparency carrying the image, so that light from a light source passes through the original image onto the light sensitive element. Since no lens systems are required and the original image is adjacent the light sensitive element, the print exhibits very low degradation from the original image.
Contact printing then, is particularly desirable in cases where it is necessary to maintain a very high resolution in the print. There are many uses of contact printing in the areas of high quality film and lithographic reproduction for images, circuit boards and integrated cicuits. Another example is in the printing of integral images. Failure to maintain a high resolution may cause individual image segments or line segments, to overlap in the print leading to an undesirable image.
Integral image elements themselves are well known. For example, known integral image elements include those which use a lenticular lens sheet, fly's eye lens sheet, or barrier strip sheet and a three-dimensional integral image aligned with the sheet, so that a user can view the three-dimensional image without any special glasses or other equipment. Such imaging elements and their construction, are described in "Three-Dimensional Imaging Techniques" by Takanori Okoshi, Academic Press, Inc., New York, 1976. Integral image elements having a lenticular lens sheet (that is, a sheet with a plurality of adjacent, parallel, elongated, and partially cylindrical lenses) are also described in the following Unites States patents: U.S. Pat. No. 5,391,254; U.S. Pat. No. 5,424,533; U.S. Pat. No. 5,241,608; U.S. Pat. No. 5,455,689; U.S. Pat. No. 5,276,478; U.S. Pat. No. 5,391,254; U.S. Pat. No. 5,424,533 and others; as well as allowed U.S. patent application Ser. No. 07/931,744. Integral image elements with lenticular lens sheets use what is referenced as a lenticular image having interlaced vertical image slices which in the case of a three-dimensional lenticular image, these image slices are aligned with the lenticules so that a three-dimensional image is viewable when the lenticules are vertically oriented with respect to a viewer's eyes. The image may be conveniently laminated (that is, adhered) to an integral or lenticular lens sheet. Similar integral image elements, such as described in U.S. Pat. No. 3,268,238 and U.S. Pat. No. 3,538,632, can be used to convey a number of individual two-dimensional scenes (such as unrelated scenes or a sequence of scenes depicting motion) rather than one or more three-dimensional images. Integral image elements using reflective layers behind the integral image to enhance viewing of the integral image by reflected light, are also described in U.S. Pat. No. 3,751,258, U.S. Pat. No. 2,500,511, U.S. Pat. No. 2,039,648, U.S. Pat. No. 1,918,705 and GB 492,186.
While contact printing an original image, such as an original image, does not produce a print with as much degradation than might occur using an enlarger for printing, for example, it is not perfect. It is known that the light source used to illuminate the original image will not illuminate the original image completely uniformly. Typically, with a projection type light source, this means that the center of the print will tend to be darker (where the print is a negative). In an attempt to correct for this, a sequence of discrete filters has been used between the light source and original image, such that overall the sequence exhibits incremental decreases in density moving from the center to the periphery. However, this technique requires manually estimating the light intensity variance at the original image position, estimating a suitable filter sequence and then constructing it. Inherent errors in these steps will inevitably lead to poor correction for light intensity variance. Additionally, at the edges of the overlapping filters there will be a sudden drop in overall density and hence a sudden drop in light intensity. The same situation is present in other types of printers, such as photographic enlargers.
It would be desirable then, to provide a means for improving illumination uniformity at the original image position in a photographic printer, which is simple to implement and which does not produce at the original image position, edges across which there is a sudden variation in light intensity.